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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

FUELS   (GENERAL METHODS)                         299

volatile matter (hydrocarbons and other organic substances). The appear-
ance of the coke is noted : whether it is pulverulent, or composed of frag-
ments more or less cemented together, or fused, and in the last case, if it
is compact or porous, and more or less swollen.

4 Determination of the Sulphur.—The sulphur contained in fuels
is present partly as sulphides (pyrites) and sulphates, and partly in organic
compounds. In the combustion part of the sulphur (that of the sulphates
and some of that of the sulphides) remains in the ash, whilst the remainder
(the organic sulphur and part of that of the sulphides) passes over among
the products of combustion (combustible, injurious or volatile sulphur)
as sulphur dioxide and, in small proportion, sulphur trioxide.

The total sulphur is determined by a slight modification of Eschka's
method, which is carried out as follows: About I gram of the finely
powdered coal (passing a sieve of 650 meshes per sq. cm.) is thoroughly
mixed in a roomy platinum crucible with about 1-5 gram of a mixture of
magnesium oxide (z parts) and dry sodium-potassium carbonate (i part)
by means of a platinum wire, about 0-5 gram of the same mixture being
then placed on the top. The open and inclined crucible is then arranged
in the hole in a piece of asbestos board and heated over a small flame so
that only its lower portion is reddened. The heating is continued for
about an hour—the mixture being frequently stirred with a platinum wire
—until the grey colour has changed uniformly to yellowish, reddish or
brown. The crucible is then allowed to cool and the contents washed with
hot water into a beaker and the liquid made feebly yellow with a little
bromine water, boiled, and filtered, the residue being washed with boiling
water. The filtrate is acidified with hydrochloric acid, boiled to expel
the remaining free bromine, and the colourless liquid precipitated with
barium chloride and the barium sulphate weighed as usual.

If the fixed and volatile sulphur are required separately, the former is
determined directly. To this end, a weighed quantity of the coal sufficient
to give 1—2 grams of ash is incinerated and the ash treated in the hot in a
porcelain dish with hydrochloric acid and a little potassium chlorate or
bromine to oxidise any sulphites formed as well as the sulphides. The
excess of chlorine or bromine is expelled by boiling, the liquid precipitated
with ammonia and filtered, and the filtrate acidified and precipitated with
barium chloride in the usual way: BaS04 x 0-1374 = S. Total sulphur
minus fixed sulphur = volatile sulphur.

5.  Determination of the Phosphorus.—This is carried out on the
ash (i—2 grams), which is digested with cone, hydrochloric acid in a porcelain
dish on a water-bath, evaporated to dryness and the residue moistened with
hydrochloric acid, diluted with water, filtered into another porcelain dish
and taken almost to dryness with several additions of nitric acid.   The
residue is then taken up in water acidified with nitric acid and precipitated
in a beaker with ammonium molybdate and so on (see Determination of
Phosphorus in Iron, p. 173).

6.  Determination of the Carbon and Hydrogen.—These are deter-
mined by the ordinary method followed for the elementary analysis of
organic substances, the substance being burnt in a current of oxygen andten : Fourth Mint Report,